1. Field of the Invention
The present invention generally relates to electrophotographic devices, and more particularly to an electrophotographic device in which a toner latent image is formed on a recording drum for imaging.
Currently, there is a demand for economical and small-size electrophotographic devices. Thus, a serial-type electrophotographic printer in which an electrophotographic unit is mounted in a carriage has been developed. In this type of electrophotographic printer, an image is transcribed on recording paper by a carriage being conveyed in a perpendicular direction to a feeding direction of the recording paper. The transcribed image is fixed by a photographic fixing device provided in the feeding direction of the recording paper. In this type of electrophotographic printer, an improvement in the quality of the recorded image is desired.
2. Description of the Prior Art
FIG. 1A is a partial plan view of a conventional serial-type electrophotographic printer and FIG. 1B is a sectional view showing a carriage thereof.
A serial-type electrophotographic printer 11 shown in FIGS. 1A and 1B is disclosed in Japanese Laid-Open patent Application No. 56-152463. The serial-type electrophotographic printer 11 is equipped with feeding rollers 13a, 13b for feeding recording paper 12 and a shaft 14 parallel to the feeding rollers 13a, 13b. A removable carriage 15, guided by the shaft 14, is provided in a perpendicular direction to the feeding direction of the recording paper 12. The carriage 15 is conveyed by a driving motor (not shown). At a downstream side in the feeding direction of the recording paper 12, there is provided a photographic fixing device 16, which is longer than the width of the recording paper 12. Also, a transcription device 17 is provided under the recording paper 12 in the feeding direction of the recording paper 12.
A drum-shaped image carrier (hereinafter simply referred to as drum) 21, which rotates at a circumferential speed in synchronism with movement of the carriage 15, is mounted in the carriage 15. A circumferential surface of the drum 21 is uniformly charged by a charging device 22 and an electrostatic latent image is formed thereon by an exposing device 23. The electrostatic latent image is made into a visible toner image by toner 25 in a developing device 24. The toner 25 is applied by a developing roller 26. The toner image is transcribed to the recording paper 12 by the transcription device 17 which faces the drum 21 on the opposite side of the recording paper 12. The transcribed portion is photographically fixed by the photographic fixing portion 16.
In this serial-type electrophotographic device 11, feeding of the recording paper is an intermittent action. Accordingly, the fixed image quality is different when the recording paper is being fed from that when the recording paper is stopped. This operation prevents a uniform fixing quality from being achieved. For example, part of the recording paper in contact with the fixing roller when the fixing roller is stopped has a glossy appearance.
In order to solve the above problem, a serial-type electrophotographic device has been developed in which a photographic fixing roller is provided in a carriage.
FIG. 2 is a schematic illustration showing a carriage in which a photographic fixing device is provided. A carriage 15 having a photographic fixing device 27 is disclosed in Japanese Laid-Open Utility Model Application No. 61-145649. In the carriage 15, a cleaner 30 is provided in order to remove toner particles remaining on the drum 21 after a printing cycle.
In the photographic fixing device 27, a fixing roller 28 is provided which rotates in the same direction as the drum 21. In the fixing roller 28, a heat source 29 (i.e. a halogen lamp) is provided. The fixing roller 28 is heated by the heat source 29 before a printing operation and the temperature thereof is detected and controlled by a temperature sensor (not shown) such as a thermistor. That is, the fixing device 27 is conveyed with the drum 21 in order to conduct the photographic fixing subsequent to the transcription of the image.
Since the transcription by the transcription device 17 is conducted by applying a prescribed electric voltage between the transcription device 17 and the drum 21, an electrically conductive material, such as electrically conductive gum, is applied on a baseboard in the photographic fixing device 17.
However, in the serial-type electrophotographic printer described above, when the carriage having an imaging unit is conveyed on the recording paper 12, the toner 25 in the developing device 24 may possibly overflow onto the recording paper 12 or the toner 25 deposited at both edges of the developing roller 26 may possible fall on the recording paper 12. This toner residue degrades the image quality.
Also, when the toner 25, deposited on both edges of the developing roller 26, is transferred to the recording drum 21, the toner 25 is gradually deposited on the charging device 22 which contacts the recording drum 21. Part of the charging device 22 on which the toner 25 is deposited cannot have a charging function. Therefore, lines are printed on the recording paper. In this case also, the image quality is degraded.